Polytrimethylene terephthalate (“PTT”) is generally prepared by the polycondensation reaction of 1,3-propanediol with terephthalic acid or terephthalic acid esters. PTT resin, when compared to polyethylene terephthalate (“PET”, made with ethylene glycol as opposed to 1,3-propane diol) or polybutylene terephthalate (“PBT”, made with 1,4-butane diol as opposed to 1,3-propane diol), is superior in mechanical characteristics, weatherability, heat aging resistance and hydrolysis resistance.
PTT, PET and PBT find use in many application areas (such as carpets, home furnishings, automotive parts and electronic parts) that require a certain level of flame retardance. It is known that PTT in and of itself may, under certain circumstances, have insufficient flame retardance, which currently limits in many of these application areas.
There have been several attempts to improve the flame retardance properties of PTT compositions through the addition of various flame retardant additives. For example, PTT compositions containing halogen-type flame retardants have been widely studied. For example, GB1473369 discloses a resin composition containing polypropylene terephthalate or PBT, decabromodiphenyl ether, antimony trioxide and asbestos. U.S. Pat. No. 4,131,594 discloses a resin composition containing PTT and a graft copolymer halogen-type flame retardant, such as a polycarbonate oligomer of decabromobiphenyl ether or tetrabromobisphenol A, antimony oxide and glass fiber.
Several attempts have been made to prepare halogen-free flame retardant polyester formulations. Processes to make polyesters flame retardant by using halogen-free flame retardants based on P-containing and N-containing compounds are well known. Thus JP-A-06/157880 describes filled polyalkylene terephthalates containing melamine cyanurate and an aromatic phosphate. JP-B-3115195 describes polyesters with N-heterocyclic compounds and a polyfunctional group compound and optionally a P-based flame retardant. U.S. Pat. No. 4,203,888 teaches a polyester with organic diphosphates. However the compositions do not good exhibit good thermal stability especially on prolonged heat aging.
EP-A-0955338, EP-A-0955333 and JP-A-07/310,284 propose PBT resin compositions containing melamine cyanurate, ammonium polyphosphate or melamine polyphosphate, phosphate ester and glass fiber. These compositions, however, have large warpage deformation and a poor appearance when molded, and thus cannot sufficiently satisfy the market's needs.
US2002/0120076A1 describes a polyester molding composition with an improved combination of flowability and mechanical properties. The molding composition comprises from 80 to 99.9 parts by weight of thermoplastic polyester and from 0.1 to 20 parts by weight of a polyamine-polyamide graft copolymer where the total of the parts by weight of the polyester and of the graft copolymer is 100. The polyamine-polyamide graft copolymer is prepared using the following monomers: (a) from 0.5 to 25% by weight, preferably from 1 to 20% by weight, and particularly preferably from 1.5 to 16% by weight, based on the graft copolymer, of a branched polyamine having at least 4 nitrogen atoms, preferably at least 8 nitrogen atoms, and particularly preferably at least 11 nitrogen atoms, and having a number-average molar mass Mn of at least 146 g/mol, preferably of at least 500 g/mol, and particularly preferably of at least 800 g/mol, and (b) polyamide-forming monomers selected from lactams, omega-aminocarboxylic acids, and/or from equimolar combinations of diamine and dicarboxylic acid.
There still is a need to provide PTT compositions with improved flame retardancy properties.